Alright, what mana link does is uses all your piety to deal that much damage to all monster and yourself to a minimum of 1 hp.

What you can do is: At level 1, cast a bunch of spells and explore without leveling up. When you reach max or close to max piety you use this ability. Then with fireball in hand (which you will probably have with all your exploration) you kill some 7/8 that has 1 hp and gain a ton of XP. This will level you up and give you back mana, allowing you to kill some high level 9s and other 8s (which still have 1 hp) for more level ups and more fireballs. When your this high level you can quickly kill off low level enemies to push to you the next level and further take advantage of the free mana from leveling. From this point reaching level 9, if not 10 is pretty easy. And killing the boss with hopefully still a good chunk of unexplored tiles and full potions pretty easy. If you time it right you can start taking down the boss while it is still hurt from this effect (plus you have more piety from all those spells).

Wow, very nice catch. I knew I wanted to try something with Mana Leak, but I kept thinking in terms of doing a bit of extra damage to the boss, or setting up a double mid-battle level-up. I hadn't thought about using it at level 1; nicely done.

That said, there's limitations on it. Level 9 enemies have 134 base health, level 8 enemies have 111 base health, level 7 enemies have 90 (although since most dungeons are still using 120% monster stats, more like 108). So...probably level 7 is the highest enemy you'll kill since you only get 100 damage (and level 7 means 42 bonus exp). This puts you probably at level 5, where you might be able to kill a level 9 enemy (20 bonus exp) probably levelling up to 6, maybe killing the second level 9 (12 bonus exp). And now you're level 6, and the highest level enemy is level 8, and at any rate you probably need to regen so your exp romp is basically done (maybe you'll get 6 bonus exp from killing a level 8 the normal way). That's 80 bonus experience. In a normal DD game you get maybe ~8 bonus exp per level by killing higher level enemies between level 2 through level 7, so you'd normally get about 48 bonus. So...80-48 = 32 more exp than you would have normally gotten.

32 exp is totally worth doing, but I'm not sure it's any better than boons offered by other deities, say, Glowing Guardian's Humility, or Pactmaker's (freeware version) "Learning" skill. It's something I definitely want to try first before assuming "overpowered". Still, definitely a better way of using Mystera than I've been doing so-far.

So...expanding a little on the bonus exp stuff...this is something I've been thinking about for a while. Sure, in the Factory in Freeware if you killed a level 9 armor at level 1, you gained tons of bonus and went straight to level 6. But then you get minimal bonus exp for the rest of the game. Assuming you can kill any enemy you want, is the 1->9 exp slingshot worth-it, given that it denies several lower level slingshots? (The answer is yes, but not by much).

So...I started to play around with "what's the most bonus exp you can get from a single map without killing a boss?", and I...think the answer is 96. (Normal amounts of bonus exp, if you're killing higher level enemies regularly, are 40-60 depending on whether the enemies you're killing are one level higher, or two levels higher).

So...something that just helps you slingshot actually has a maximum exp cap. An ability that does extra (like the Fighter's bonus exp, or Glowing Guardian keeping you at an artificially low level so that you can slingshot over and over) are the kind of things you need if you want to break this natural exp cap.

Despite doing all the levels (except mr. 50 levels of death protection) I've only unlocked 2 deities (thief and wizard ones). I failed twice on the priest one, and never saw the fighter one (despite using warlord a lot).

I don't want to see this type of strat usable on almost all dungeons though. A few is fine, but having a single trick to beat most dungeons should probably be discouraged. In any case I find using this works quite well if you are up against debuff enemies (weaken, manaburn, poison) as you usually want to kill those to level up (except weaken) not in between levels. If you had a specialized dungeon with lots of high hp (zombies meat man), or one that prevented you from fighting much stronger enemies until you kill weaker ones, the strategy might fall though.

Funny you should add a quest for Assassins in Creeplight when that's just what I've been working on. Even after today's changes my strategy still works:

It's not displayed in the results, but I believe I killed Anoobis' first form at level 3 or so, with poison + fireballs, then used Mana Leak and first strike to level up while continuing to fireball him to death. Note that this was with the boss at edge of the screen, meaning no first strike against him (that's a bug that will be fixed, right? I don't like that at all) and using Mana Leak made Mystera angry and gave everything extra magic resist for some unknown reason. Plus, this was with a mere 60 piety Mana Leak, and I didn't have BLOODTOPOWA or IMAWALL (which are two of the most helpful glyphs in this strategy). I don't think Mana Leak necessarily needs a huge nerf, especially since classes other than Assassin and possibly Rogue will have a harder time exploiting it and Creeplight is fairly unique in having no enemies with first strike or physical resistance which would both pose difficulties, but decreasing the ratio of damage done to 3/4 piety or maybe even 1/2 piety would probably be a good idea.